This invention relates to electrical switches, and more particularly to an electrical switch of the type having stationary spaced apart first and second contact areas and a stationary center contact area located therebetween, in combination with a movable contact member for selectively establishing an electrical path between the center contact area and either the first stationary contact area or the second stationary contact area.
Typical single-pole double-throw (SPDT) switches are used to alternately connect two different loads to a single power source. A typical SPDT switch includes a housing to which a generally U-shaped center contact saddle is mounted, in combination with spaced apart first and second contacts located on opposite sides of the center contact saddle. A movable contact, which is generally L-shaped or V-shaped, is engaged with the center contact saddle and is movable between a first operative position and a second operative position. In the first operative position, a movable contact carried by a first leg of the movable contact member is engaged with the first stationary contact, to establish an electrical path between the first stationary contact and the center contact saddle. In the second operative position, a movable contact carried by a second leg of the movable contact member is engaged with the second stationary contact, to establish an electrical path between the second stationary contact and the center contact saddle. A movable actuator is mounted to the housing for moving the movable contact member between the first and second operative positions, and to an inoperative position in which neither of the movable contacts is engaged with its respective stationary first or second contact.
Typically, it has been known to increase the number of stationary contacts and movable contact members in order to increase the current-carrying capacity of the switch, since increasing the size of the stationary contacts and/or the movable contact member does not in and of itself serve to increase current-carrying capacity. In the prior art, this results in a switch such as is illustrated in Krause U.S. Pat. No. 4,789,766 as well as various other prior art patents. Solutions of this type involve increasing the number of stationary first, second and center contacts, and providing an additional movable contact member for each additional set of stationary first, second and center contacts. The switch actuator includes a separate biased plunger member for each movable contact member, such that the movable contact members move in unison between the first and second operative positions in response to movement of the switch actuator. While this type of switch construction serves to increase current-carrying capacity, it involves certain drawbacks and also limits the applications in which this type of switch can be used. For example, this construction provides a one-to-one ratio between the number of stationary center contacts and the number of stationary first and second contacts. Further, this construction entails additional components, which provides a corresponding increase in the number of assembly steps and thereby the cost of manufacture of the switch. Most importantly, however, this construction creates the potential for the separate movable contact members to be in opposite operative positions. For example, in the event one of the contacts of one of the movable contact members becomes welded to one of the stationary contacts, or becomes jammed or otherwise stuck in one position, it is possible for the other of the movable contact members to be moved to the opposite operative position independently of the movable contact member that is prevented from movement. This can result in two loads being effectively connected to the single power source at the same time, which is typically undesirable in the circuit in which this type of switch is employed. Furthermore, this construction prevents a switch of this type from being used as a transfer switch, in which the switch is used to alternately connect a single load to either a first power supply or a second power supply. In an application such as this, it is essential that there can be no possibility for the load to be connected to both power supplies at the same time due to the relatively serious consequences which could result from such an occurrence.
It is an object of the present invention to provide an electrical switch which utilizes a similar overall construction and operation as prior art switches of the type described above, and which incorporates a feature that ensures the movable contact member cannot be in a position in which contact is simultaneously established between the center contacts and both the first and second stationary contacts on either side of the center contacts. It is a further object of the invention to provide such an electrical switch which is thus capable of being used as a transfer switch, to alternately connect a load with one of two available power sources. A still further object of the invention is to provide such an electrical switch which produces minimal arcing or bouncing of the movable contact member during movement between the first and second operative positions, to maintain full contact with the stationary center contact arrangement. A still further object of the invention is to provide such an electrical switch which ensures an equal distribution of current as the current flows through the movable contact member. A still further object of the invention is to provide such an electrical switch which is relatively simple in its components and construction, yet which functions in a highly satisfactory manner to either selectively connect one of two loads with a power source, or to act as a transfer switch that selectively connects a load with one of two power sources.
In accordance with the invention, an electrical switch includes a housing, and spaced apart sets of stationary first and second contacts are mounted to the housing. A stationary center contact arrangement is mounted to the housing, and is located between the sets of stationary first and second contacts. A movable contact member is contained within the housing, and an actuator is engaged with the movable contact member for moving the movable contact member between a first operative position in which the movable contact member establishes an electrical path between the stationary center contact arrangement and the set of stationary first contacts, and a second operative position in which the movable contact member establishes an electrical path between the stationary center contact arrangement and the set of stationary second contacts. The movable contact member includes a common central contact area which is engaged with the stationary center contact arrangement, in combination with a number of separate first arms that extend outwardly from the center contact area in a first direction, and a number of separate second arms that extend outwardly from the center contact area in a second direction opposite the first direction. The number of first and second arms corresponds to the number of stationary first and second contacts, respectively. With this construction, each of the first arms establishes an electrical path between the center contact arrangement and one of the stationary first contacts when the movable contact member is in the first operative position, and each of the second arms establishes an electrical path between the center contact arrangement and one of the stationary second contacts when the movable contact member is in the second operative position.
The center contact arrangement may be in the form of a series of spaced apart center contact members, and the center contact area of the movable contact member spans between and engages the spaced apart center contact members. In a preferred form, the center contact members define coplanar flat contact surfaces, and the center contact area of the movable contact member defines a rocking center contact construction which remains in engagement with the flat contact surfaces of the spaced apart center contacts during movement of the movable contact member between its first and second operative positions. The number of center contact members may be the same, greater or less than the number of stationary first and second contacts.
The movable contact member is preferably constructed such that the first and second sets of arms are formed integrally with the center contact area. The center contact area is preferably defined by intersecting first and second planar sections which cooperate to define a V-shape, and the point of intersection of the first and second sections forms a fulcrum that rests on the contact surfaces of the stationary center contact members. The set of first arms are preferably in the form of outward extensions of the first center contact section, and the set of second arms are preferably in the form of outward extensions of the second center contact section. The sets of first and second arms are preferably separated from each other by a gap or space located outwardly of an intermediate portion of the center contact area located between adjacent first arms and adjacent second arms.
Each of the first and second arms is flexible and resilient, and the actuator includes a separate actuating member that engages each of the first arms when the movable contact member is in the first operative position, and that engages each of the second arms when the movable contact member is in the second operative position. Each actuating member is preferably in the form of a biased plunger which exerts a force on the first arm of the movable center contact member when the movable contact member is in the first operative position, and on the second arm of the movable contact member when the movable contact member is in the second operative position. Each of the first and second arms is flexible and resilient, such that application of the force on each arm by the actuator member is operable to ensure proper fill contact of each arm with its respective stationary contact.
The center contact area provides a common connection of each of the first and second arms, to ensure proper current sharing when the movable contact member is in either the first operative position or the second operative position. In addition, the construction of the movable contact member, in which the arms extend from a common center contact area, ensures that it is impossible for the movable contact member to be in a position in which both the first and second contacts are electrically connected to the center contact arrangement at the same time, to enable the switch to be utilized as a transfer switch.